Diamond design chair back



FIG. 1 is a top right perspective view of a chair back showing my ornamental design.

FIG. 2 is a bottom left perspective view thereof.

FIG. 3 is an enlarged view of the chair back of FIG. 1 taken generally from circle 3 of FIG. 1.

FIG. 4 is an enlarged view of a portion of the chair back of FIG. 1 taken generally from circle 4 of FIG. 1.

FIG. 5 is an enlarged view of a portion of the chair back of FIG. 1 taken generally from circle 5 of FIG. 1. 

The ornamental design for diamond design chair back, as shown and described. 